The invention relates to the general field of communications by radio.
More particularly, it relates to communications, e.g. radio communications, between objects or pieces of equipment connected to a communications network (also referred to as “connected objects”) and deployed in a geographical area of greater or lesser extent.
The invention applies more particularly in the context of networks of connected objects of the Internet of things (IoT) type or the machine to machine (M2M) type in which data is collected continuously, using a dedicated underlying infrastructure of a service provider suitable for providing the data as connected in this way to one or more clients. The infrastructure is made up in particular of receiver stations referred to as digitizing stations or as receiver equipment that serve to collect data and transmit it in the form of packets of digital samples to a computer system of a client of the service provider. The digital samples are indexed in the computer system in a database using various criteria, such as the criteria of time, place, and frequency. Application EP 2 728 909 describes one such infrastructure.
It can thus be understood that localization both in time and in space is key for networks of connected objects that use indexing based on criteria of that type. Such localization relies in particular on timestamping digital samples. In the meaning of the invention, “timestamping data” covers associating such data with an accurate timestamp, e.g. in the form of a date (year, month, day) and a time (hours: minutes: seconds).
In the present state of the art, data is timestamped in the digitizing receiver stations while forming packets of digital samples. For this purpose, each receiver station needs to be fitted with a synchronizer device suitable for recovering a time reference locally (e.g. a common clock broadcast by a global positioning system (GPS) signal, or a radio control clock), to synchronize the time reference relative to the digital sampling clock of the digitizing receiver station, to extract timestamping information established on the basis of the synchronized common time reference and to associate that information with the samples, and to integrate that information in the headers of packets of samples for transmitting to the computer system.
Depending on the desired accuracy of timestamping, those operations impose major hardware and/or software constraints on the receiver stations and can lead to non-negligible implementation costs.
In addition, that complexity and those costs need to be met by the receiver stations even if, in the end, the timestamping information is not used by the information system of the client of the service provider.